Role of epoxyeicosatrienoic acids in protecting the myocardium following ischemia/reperfusion injury

Abstract

Cardiomyocyte injury following ischemia-reperfusion can lead to cell death and result in cardiac dysfunction. A wide range of cardioprotective factors have been studied to date, but only recently has the cardioprotective role of fatty acids, specifically arachidonic acid (AA), been investigated. This fatty acid can be found in the membranes of cells in an inactive state and can be released by phospholipases in response to several stimuli, such as ischemia. The metabolism of AA involves the cycloxygenase (COX) and lipoxygenase (LOX) pathways, as well as the less well characterized cytochrome P450 (CYP) monooxygenase pathway. Current research suggests important differences with respect to the cardiovascular actions of specific CYP mediated arachidonic acid metabolites. For example, CYP mediated hydroxylation of AA produces 20-hydroxyeicosatetraenoic acid (20-HETE) which has detrimental effects in the heart during ischemia, pro-inflammatory effects during reperfusion and potent vasoconstrictor effects in the coronary circulation. Conversely, epoxidation of AA by CYP enzymes generates 5,6-, 8,9-, 11,12- and 14,15-epoxyeicosatrienoic acids (EETs) that have been shown to reduce ischemia-reperfusion injury, have potent anti-inflammatory effects within the vasculature, and are potent vasodilators in the coronary circulation. This review aims to provide an overview of current data on the role of these CYP pathways in the heart with an emphasis on their involvement as mediators of ischemia-reperfusion injury. A better understanding of these relationships will facilitate identification of novel targets for the prevention and/or treatment of ischemic heart disease, a major worldwide public health problem.

Full text

Role of epoxyeicosatrienoic acids in protecting the myocardium
following ischemia/reperfusion injury
John M. Seuberta,*, Darryl C. Zeldinb, Kasem Nithipatikomc, and Garrett J. Grossc
a Faculty of Pharmacy and Pharmaceutical Sciences, 3126 Dentistry/Pharmacy Centre, University of Alberta,
Edmonton, AB, Canada T6G 2N8
b Division of Intramural Research, NIEHS/NIH, Research Triangle Park, NC 27709, USA
c Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
Abstract
Cardiomyocyte injury following ischemia–reperfusion can lead to cell death and result in cardiac
dysfunction. A wide range of cardioprotective factors have been studied to date, but only recently
has the cardioprotective role of fatty acids, specifically arachidonic acid (AA), been investigated.
This fatty acid can be found in the membranes of cells in an inactive state and can be released by
phospholipases in response to several stimuli, such as ischemia. The metabolism of AA involves the
cycloxygenase (COX) and lipoxygenase (LOX) pathways, as well as the less well characterized
cytochrome P450 (CYP) monooxygenase pathway. Current research suggests important differences
with respect to the cardiovascular actions of specific CYP mediated arachidonic acid metabolites.
For example, CYP mediated hydroxylation of AA produces 20-hydroxyeicosatetraenoic acid (20-
HETE) which has detrimental effects in the heart during ischemia, pro-inflammatory effects during
reperfusion and potent vasoconstrictor effects in the coronary circulation. Conversely, epoxidation
of AA by CYP enzymes generates 5,6-, 8,9-, 11,12- and 14,15-epoxyeicosatrienoic acids (EETs) that
have been shown to reduce ischemia–reperfusion injury, have potent anti-inflammatory effects
within the vasculature, and are potent vasodilators in the coronary circulation. This review aims to
provide an overview of current data on the role of these CYP pathways in the heart with an emphasis
on their involvement as mediators of ischemia–reperfusion injury. A better understanding of these
relationships will facilitate identification of novel targets for the prevention and/or treatment of
ischemic heart disease, a major worldwide public health problem.
Keywords
Arachidonic acid; Cytochrome P450; Eicosanoids; Ischemia reperfusion injury; Cardioprotection
1. Introduction
Heart disease and stroke are major causes of illness, disability and death in Western societies,
and impose a great burden to national health care systems [1-6]. For example, cardiovascular
disease (CVD) accounted for the death of approximately 76,500 Canadians in 2002 [2,4] and
over 910,000 individuals in the US [6]. As the population ages and co-morbidities, such as
obesity and diabetes become more prevalent, both the human cost and economic burden of
CVD will likely increase. Acute myocardial infarction (AMI) continues to be a leading cause
of death worldwide [7,8]. Myocardial infarction occurs when ischemia exceeds a critical
threshold and overwhelms cellular repair mechanisms that are designed to maintain normal
operating function and homeostasis. Ischemia at this critical threshold level results in
* Corresponding author. Tel.: +1 780 492 0007; fax: +1 780 492 1217. E-mail address:jseubert@pharmacy.ualberta.ca (J.M. Seubert).
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Published in final edited form as:
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irreversible myocardial cell damage or death. Such injury contributes to the pathogenesis of
heart failure (HF), AMI and sudden death [9]. Advances in early reperfusion therapy, such as
thromobolytic drugs, coronary angioplasty or bypass graft surgery, have reduced morbidity,
HF and infarct-associated ventricular arrhythmias. Preconditioning (PC) is another powerful
cardioprotective strategy that renders the heart resistant to injury [10]. Brief, non-detrimental
episodes of ischemia or pharmacological mimetics given prior to a prolonged ischemic event
can initiate signaling events that protect the myocardium [10]. Unfortunately, both early
reperfusion therapy and cardioprotective drugs given prior to ischemia have limited clinical
utility as patients typically present after the onset of ischemia and/or are unable to reach medical
facilities [11,12]. In light of the increasing incidence and prevalence of HF after AMI [1,3,4],
there is a profound need for a better understanding of the underlying pathophysiology and a
need for development of strategies to protect the myocardium from ischemic-reperfusion
injury. Thus, novel therapeutic strategies are required in order to prevent the adverse
consequences and impact of CVD.
2. Arachidonic acid, CYP epoxygenases and soluble epoxide hydrolase
Arachidonic acid (AA), a polyunsaturated fatty acid normally found esterified to cell
membrane glycerophospholipids, can be released by phospholipases in response to several
stimuli, such as ischemia [13]. Free AA is then available for metabolism by prostaglandin H2
synthases, lipoxygenases and cytochrome P450 monooxygenases to generate numerous
metabolites, collectively termed eicosanoids [14,15]. CYP epoxygenases metabolize AA to
four regioisomeric epoxyeicosatrienoic acids (5,6-, 8,9-, 11,12- and 14,15-EETs), all of which
are biologically active (Fig. 1) [16,17]. The actions of EETs are terminated by conversion to
the corresponding and less biologically active dihydroxyeicosatrienoic acids (DHETs) by
epoxide hydrolases [13]. Two major epoxide hydrolases are found in mammalian tissues, the
microsomal epoxide hydrolase (mEH) and the soluble epoxide hydrolase (sEH or EPHX2)
[14]. Previous work has demonstrated that sEH is the main enzyme involved in the in vivo
hydrolysis of the EETs [15,17]. The majority of endogenous EETs (>85%) are esterified to
membrane glycerophospholipids, particularly phosphatidylcholine and phosphatidylinositol,
where they are generally considered inactive until their release [17]. In this regard, ischemia
has been shown to activate cytosolic phospholipase A2 leading to the release of bioactive
eicosanoids from glycerophospholipids [18].
EETs are important components of many intracellular signaling pathways in both cardiac and
extracardiac tissues. For example, EETs activate Ca2+-sensitive K+ channels (BKCa) in
vascular smooth muscle cells resulting in hyperpolarization of the resting membrane potential
and vasodilation of the coronary circulation [19-21]. This effect is diminished upon hydrolysis
of EETs to DHETs by sEH [22]. Other studies have shown that EETs display anti-
inflammatory, thrombolytic and angiogenic properties within the vasculature [23-25]. In
endothelial cells, EETs activate mitogen activated protein kinase (MAPK) and
phosphatidylinositol-3 kinase (PI3K)-Akt signaling pathways [25], increase intracellular
cAMP levels [24], upregulate expression of nitric oxide synthase [26] and protect against
hypoxia-reoxygenation injury [27]. In general, the effects of DHETs on these pathways are
less pronounced [23,24]. Within the heart, EETs activate cardiac ATP-sensitive K+ (KATP)
channels [28-31], enhance L-type calcium currents [32,33] and improve postischemic recovery
of left ventricular function [31,34-36]. Thus, alteration in the production and/or elimination of
EETs may affect steady-state cellular levels of these bioactive eicosanoids in vivo and could
potentially influence cardiac function (Fig. 2).
Arachidonic acid can be metabolized by CYP epoxygenases and CYP ω-hydroxylases to
products that have vastly different physiologic effects. For example, EETs have potent
vasodilatory properties [37] and 20-hydroxyeicosatetraenoic acid (20-HETE) has potent
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vasoconstrictive effects [38]. Therefore, changes in the expression and/or activity of specific
CYP epoxygenase and hydroxylase enzymes can alter the delicate balance between EETs and
20-HETE. For instance, recent data has demonstrated that inhibition of CYP ω-hydroxylases
results in reduction of infarct size in rats and dogs following ischemic injury, which suggests
that 20-HETE has detrimental effects in the heart [39,40]. These investigators originally
showed that 20-HETE was released into coronary venous blood in high concentrations at the
end of 60 min of ischemia and throughout 3 h of reperfusion. Furthermore, the non-selective
CYP inhibitor, miconazole (MIC) and the more selective inhibitors, 17-octadecanoic acid (17-
ODYA) and N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), all reduced 20-
HETE release from the ischemic/reperfused heart and produced marked reductions in
myocardial infarct size (expressed as a percent of the area at risk) from 19.6 ± 1.7% to 8.4 ±
2.5% (MIC), 5.9 ± 2.2% (17-ODYA) and 10.8 ± 1.8% (DDMS), respectively [39,40].
Conversely, exogenous administration of 20-HETE significantly increased infarct size to 26.9
± 1.9%. These investigators also showed that at least three isoforms of the ω-hydroxylases
were present in canine heart tissue – CYP4A1, CYP4A2 and CYP4F – all of which were
markedly inhibited by incubation with 17-ODYA. Reductions in infarct size were also
observed by this same group in rat hearts in which MIC,17-ODYA and DDMS were
adminstered prior to ischemia or 5 min prior to reperfusion [40] These results suggest that the
major effect of inhibiting ω-hydroxylase in rats occurs during reperfusion and is associated
with in a decrease in “reperfusion injury” More recently, this same group demonstrated that
inhibition of ω-hydroxylases in dog hearts with DDMS reduced infarct size to a degree equal
to that of ischemic PC, the “gold standard” in cardioprotection research. These same
investigators found that the administration of the 20-HETE antagonist, 20-HEDE, reduced
infarct size similar to that observed with ischemic PC and DDMS. Interestingly, the
combination of ischemic PC and DDMS produced a significantly greater reduction in infarct
size than either intervention alone. Together, the results suggest that these two treatments may
be acting via different signaling pathways and may be a potent combination in alleviating the
sequelae of ischemia and/or reperfusion injury in a clinical setting, such as coronary artery
bypass graft surgery.
Transgenic hearts from mice overexpressing human CYP2J2 have improved postischemic
functional recovery as evidenced by studies using Langendorff perfused hearts subjected to
ischemia/reperfusion injury [31]. Perfusion with the selective P450 epoxygenase inhibitor N-
methylsulphonyl-6-(2-proparglyloxyphenyl)hexanamide (MS-PPOH) for 20 min prior to
ischemia resulted in reduction of postischemic LVDP recovery in wild type hearts and
abolished the improved postischemic LVDP recovery in CYP2J2 transgenic hearts. These data
provided evidence that the cardioprotective effects of CYP2J2 overexpression involved P450
epoxygenase metabolites. Moreover, these data suggest an important role for endogenous P450
epoxygenases in postischemic functional recovery. Mechanistic studies by these investigators
[31] suggested that enhanced activation of ATP-sensitive K+ channels (KATP) were involved
in the improved recovery observed in the CYP2J2 transgenic mice. In addition, CYP2J2
overexpressing mice exhibited increased expression of phospho-p42/p44 mitogen-activated
protein kinase (MAPK) following ischemia. The addition of the p42/p44 MAPK kinase (MEK)
inhibitor PD98059 during reperfusion abolished the cardioprotective effects observed in the
CYP2J2 mice. Together, these data suggest that CYP2J2-derived metabolites are
cardioprotective following ischemia and the mechanism for this cardioprotection involves
activation of KATP channels and p42/p44 MAPK.
Many CYP inhibitors lack isoform specificity and also may have effects on other signaling
pathways. Reduction in infarct size observed in rat and rabbit hearts following treatment with
non-specific CYP inhibitors has been attributed to suppression of CYP-dependent ROS
production [41]. CYP2C and CYP2J isozymes are the predominant AA epoxygenases in the
cardiovascular system. While CYP2C9 has been shown to generate ROS in coronary arteries
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[42], CYP2J2 is not a relevant source of ROS [27,42]. These studies highlight the complexity
of the CYP enzyme system, emphasize the role of different CYP metabolites in
cardioprotection and suggest caution in the interpretation of results when using non-selective
CYP inhibitors. Recent epidemiologic data suggests an association between single nucleotide
polymorphisms in the genes encoding CYP2J2, CYP2C8, CYP2C9 and EPHX2 and
cardiovascular disease risk in humans supporting the functional relevance of the CYP
epoxygenase pathway in the heart [43-47].
3. Ischemic injury and cardioprotection
Ischemic heart disease is an underlying cause of most AMIs, congestive HF, arrhythmias and
sudden cardiac death. Myocardial ischemia is characterized by inadequate blood flow to the
heart resulting in limited glucose, oxygen and delayed metabolic by-product removal.
Ultimately, ischemic events result in cellular death and myocyte loss which is the primary
pathology behind many CVDs. Myocytes are not easily replaced, although stem cell therapy
shows great initial promise in overcoming this problem. Nevertheless, preserving the viability
of ischemic myocardium is the major goal for cardioprotection. Cardioprotective mechanisms
modulate cell metabolism or signaling pathways directly or via posttranslational modification
of key proteins, as well initiate new transcription and translation [10,12]. A diverse spectrum
of signals converge onto a few common end effectors that maintain membrane integrity and
inhibit cell death [48]. Mitochondria are one of these important convergence points, due to
their critical function in cell survival and death; notably, ATP production and apoptosis [10,
12,48]. Key mitochondrial proteins, such as several potassium (K+) channels [49-53] and the
mitochondrial permeability transition pore (mPTP) [48,54-56], act as effectors integrating
these upstream signals into cardioprotective responses. The mechanisms by which CYP
metabolites alter these important effectors are not well defined and require further
experimentation.
3.1. K+ channels and cardioprotection
K+ channels are membrane proteins involved in many physiological processes, such as
regulation of heart rate, muscle contraction and cell volume [57]. Two pharmacologically
distinct ATP-sensitive potassium channels (KATP) have been identified in cardiomyocytes,
sarcolemmal KATP (Sarc KATP) and mitochondrial KATP (mito KATP) [58]. sarc KATP is
activated during cardiac ischemia when cytoplasmic ATP is depleted and this affects membrane
excitability. Activation leads to shortening of the cardiac action potential and reduced
intracellular calcium overload [59,60]. Although there are no selective sarc KATP openers, a
number of drugs known to open this channel have been shown to produce beneficial effects in
the myocardium in animal models of ischemia/reperfusion injury, and several non-selective
inhibitors of sarc KATP (such as glibenclamide) block ischemic PC [59,60]. In spite of these
findings, the strongest evidence for a role of sarc KATP channels in ischemic PC has been
demonstrated in the KiR 6.2 knockout mouse where ischemic PC could not be produced [60].
The EETs have been shown to be potent openers of sarc KATP by reducing channel sensitivity
to ATP in isolated rat myocytes using the inside-out patch clamp technique; however, the exact
site on the channel that interacts with EETs remains unknown [30,61]. These authors also
showed that membrane hyperpolarization occurred in isolated rat myocytes by 11,12-EET
addition, an effect blocked by glibenclamide, the non-selective KATP channel inhibitor. A role
for the sarc KATP channel in mediating the cardioprotective effect of inhibiting ω-hydroxylase
at the time of reperfusion in the rat heart was recently described [34]. These investigators
showed that the cardioprotective effect resulting from administering MIC and 17-ODYA just
prior to reperfusion in rats was completely abolished by HMR 1098, a selective inhibitor of
the sarc KATP channel. In contrast, the selective mito KATP channel inhibitor, 5-
hydroxydecanoic acid (5-HD), had no effect. Although it can be assumed that a shift in the 20-
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HETE/EET balance in favor of the EETs is responsible for the cardioprotective effect of
inhibiting 20-HETE synthesis, it remains unknown if the cardioprotective effect of the ω-
hydroxylase inhibitors is the result of the action of the EETs on the sarc KATP channel in the
myocardium.
In contrast to the sarc KATP channel, the precise molecular composition of the mito KATP
channel remains elusive. However, recent studies suggest it is part of a multiprotein complex
including the adenine nucleotide transporter (ANT) and succinate dehydrogenase (SDH)
[62]. Importantly, pharmacologic data indicate that selective activation of mito KATP confers
cardioprotection following ischemia and that this channel is the major one mediating ischemic
PC [59,60,63,64]. While the precise pathways by which mito KATP activation confers
cardioprotection remain unknown, potentially beneficial consequences of opening mito
KATP include partial depolarization of the intramitochondrial membrane, transient swelling of
the intramitochondrial space, enhanced respiration via the electron transport chain, reduced
mitochondrial calcium overload, and altered production of reactive oxygen species [59,60,
64]. Cardioprotective effects of CYP2J2 overexpression involve activation of mito KATP
channels [31]. Increased flavoprotein fluorescence (a marker of mitochondrial redox status)
[63] in CYP2J2 Tr cardiomyocytes is consistent with enhanced mito KATP activation in the
presence of CYP2J2 overexpression [31]. Moreover, treatment of wild type cardiomyocytes
with physiologically relevant concenrations of EETs increased flavoprotein fluorescence
[31].
Ca2+-activated K+ (KCa) channels include large conductance (BKCa), voltage-sensitive K+
selective proteins expressed in various tissues including heart mitochondria [53]. KCa channels
can be activated by elevations in intracellular Ca2+ and membrane depolarization [65,66]. CYP
epoxygenase derived EETs are known activators of BKCa channels in vascular smooth muscle
[20,67], whereas, CYP ω-hydroxylases derived HETEs are known inhibitors in vascular
smooth muscle [38,68,69]. Recent evidence suggests that newly identified KCa channels in
cardiac mitochondria (mito KCa) [53,70] are important mediators of cardioprotection. It is
proposed that these mitochondrial K+ channels work in concert with mito KATP and other
mitochondrial proteins in response to ischemia [49]. Activation of K+ channels by kinases,
such as PKC or PKA, and other unknown signals is predicted to increase mitochondrial K+
uptake and in turn reduce Ca2+ overload in cardiomyocytes. The cardioprotective mechanisms
associated with opening of these channels include a mild uncoupling, depolarization of the
intramitochondrial membrane, transient swelling of the intramitochondrial space, enhanced
respiration via the electron transport chain and altered production of reactive oxygen species
[49,53,59,60,64,70].
3.2. Mitochondrial permeability transition pore
mPTP is a protein complex on the inner mitochondrial membrane which includes ANT,
cyclophilin D and the voltage-dependent anion channel (VDAC) [48,49,71]. mPTP remains
closed under normal physiological conditions but opens under cellular stress, such as during
reperfusion following an ischemic event [48,49,54]. Opening allows free passage of molecules
>1.5 kDa which initiate adverse effects, like large osmotic pressure changes and uncoupling
of oxidative phosphorylation, that ultimately result in cell death [48,72]. Mitochondrial Ca2+
overload, oxidative stress, adenine nucleotide depletion and mitochondrial depolarization
contribute to the pore opening. Inhibition of prolonged mPTP opening (high-conductance)
during reperfusion with cyclosporine-A (CsA) or sanglifehrin-A (SfA) can reduce
cardiomyocyte injury [73-75]. Conversely, evidence suggests that the transient (low-
conductance) opening of mPTP during ischemic PC plays a role in cell survival [54]. Cell
culture experiments suggest that mito KATP openers, such as diazoxide, trigger mPTP opening
which can be blocked by CsA or 5HD [54]. Recent evidence demonstrates that multiple
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cardioprotective kinases, PKA, PKB/Akt and PKC can converge upon glycogen synthase
kinase-3β (GSK-3β), which will induce inhibition of the mPTP [76]. While it is very likely
that signaling pathways involved in EET-mediated cardioprotection target the mitochondria,
it is unknown whether the response involves transient opening of mPTP prior to ischemia or
prevents prolonged opening during reperfusion. EETs have been shown to activate sarc
KATP [30,61] and mito KATP channels [31] in the heart, and KCa channels [20,67], in vascular
smooth muscle cells [38,68,69]. Increased flavoprotein fluorescence in CYP2J2 Tr
cardiomyocytes and wild type cardiomyocytes treated with EETs [31], strongly suggest
convergence of a cardioprotective signal onto the mitochondria. It is expected that EETs will
alter the flavin nucleotide fluorescence and intracellular [Ca2+] within the myocytes and most
likely alter mPTP opening. It is unknown whether EETs work solely via mito KATP channels;
however, it is likely they work together with other proteins, such as mito KCa channels. Future
experiments will help determine whether EETs influence the transient opening or closing of
mPTP, as well how they influence intramitochondrial [Ca2+] levels.
4. Cardioprotective signaling pathways
There is considerable controversy regarding the role of cytochrome P450s in the heart, notably
the beneficial versus the detrimental effects of arachidonic acid metabolites [31,34,35,39,40,
77,78]. We have demonstrated that EETs play a significant role in the improved postischemic
functional recovery in isolated mouse hearts overexpressing CYP2J2 [31,34,35,57,78]. Recent
results suggest potential cardioprotective mechanisms and indicate that KATP channels, p42/
p44-MAPK and PI3K are involved. However, as previously discussed EETs are known to
activate a number of signaling elements and ion channels, therefore, further work needs to be
done to determine the important protective mediators involved in this novel cardioprotective
pathway. Preliminary data suggested that EETs might only partially activate [31] the mito
KATP channel and could be working synergistically with other cardioprotective sites, such as
the sarc KATP channel or the mito KCa channel. Additional evidence has demonstrated an
important role for PKA and PKC in the cardioprotective pathway involving K+ channels [79,
80,81]. Further experiments will help determine if EET-mediated cardioprotection involves
early activation or co-localization of PKA or PKC to the mitochondria.
5. Conclusion
There are numerous reasons for investigating the role of this novel endogenous pathway in
myocardial function and ischemic injury. First, CYP-derived metabolites of arachidonic acid
play critical roles in modulating fundamental biological processes [68,82]. Second,
environmental or genetic factors that alter P450 expression and/or function lead to changes in
the production of bioactive eicosanoids [68,82]. Such effects can influence cell and organ
function in either an adverse or beneficial manner. Third, CYP isozymes expressed in the heart,
notably CYP2J2 [36,83], generate EETs, which have been shown to be cardioprotective [31,
36,83]. In contrast, other CYP isozymes (CYP2C and CYP4A) generate products, which are
thought to be detrimental to the heart, such as ROS and 20-HETE [39-42]. Traditionally,
investigation into the role of CYP isozymes has focused on hepatic and renal drug metabolism
and function. There is little known about the importance of this endogenous system within the
heart even though the heart contains significant levels of functionally active CYP. Finally, and
most importantly, recent human epidemiological evidence has identified associations between
CYP2J2 polymorphisms and CAD, and EPHX2 polymorphisms and CHD [43,45,46,84]. These
findings provide strong evidence supporting the notion that EETs play an important role in
postischemic functional recovery and perhaps infarct size reduction [31,33,36,83]. Recent
studies have only begun to address the underlying mechanisms of EET-mediated
cardioprotection and highlight the potential for this novel endogenous system as a therapeutic
target for CVD. Ultimately, understanding the basic cellular mechanisms of EET-mediated
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cardioprotection will enhance our knowledge of this important phenomenon and will lead to
the development of novel therapeutics for the treatment of cardiovascular diseases. Targeting
CYP2J2, ω-hydroxylases or sEH, either through pharmacological or gene therapy methods,
represents a novel therapeutic approach to the management of ischemic heart disease in
humans.
Abbreviations
AA, arachidonic acid; AMI, acute myocardial infarction; ANT, adenine nucleotide transporter;
BKCa, large conductance calcium activated potassium channels; CYP, cytochrome P450
monooxygenase; CVD, cardiovascular disease; DHET, dihydroepoxyeicosatrienoic acid;
EETs, epoxyeicosatrienoic acid; GSK-3β, glycogen synthase kinase-3β; 20-HETE, 20-
hydroxyeicosatetraenoic acid; HF, heart failure; IPC, ischemic preconditioning; IR, ischemic-
reperfusion; KATP, ATP-sensitive potassium channel; KCa, calcium-activated potassium
channel; LVDP, left ventricular developed pressure; MAPK, mitogen activated protein kinase;
mEH, microsomal epoxide hydrolase; mito KATP, mitochondrial ATP-sensitive potassium
channel; mPTP, mitochondrial permeability transition pore; MS-PPOH, N-methylsulphonyl-6-
(2-proparglyloxyphenyl) hexanamide; PKA, protein kinase A; PKC, protein kinase C; PI3K,
phosphatidylinositol-3 kinase; sarc KATP, sarcolemmal ATP-sensitive potassium channel;
sEH/Ephx2, soluble epoxide hydrolase; SDH, succinate dehydrogenase; VDAC, voltage-
dependent anion channel.
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Fig. 1.
CYP epoxygenase and hydroxylase mediated metabolism of arachidonic acid.
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Fig. 2.
Schematic of proposed mechanisms of EET-mediated cardioprotection. CYP2J2-derived
eicosanoids, readily removed by sEH, activate K+ channels, p42/p44-MAPK, PKA and/or PKC
pathways leading to cardioprotection.
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